通信工程文献翻译——摘要：IEEE已经对无线局域网的802.11协议进行了标准化。802.11的主要介质访问控制（MAC）技术称为分布式协调功能（DCF）。DCF是具有二进制时隙指数退避的具有冲突避免（CSMA / CA）方案的载波侦听多路访问。本文提供了一种简单但却非常准确的分析模型来计算802.11 DCF吞吐量，假设有限数量的终端和理想的信道条件。所提出的分析适用于DCF采用的分组传输方案，即基本接入和RTS / CTS接入机制。另外，它也适用于两种方案的组合，其中根据RTS / CTS机制发送长于给定阈值的分组。通过提出的模型，我们为802.11协议的访问机制提供了广泛的吞吐量性能评估。

关键字：802.11，防碰撞，CSMA，性能评估。

一.引言

近几年来，许多兴趣已经涉及无线局域通信网络的设计[1]，[2]。研究组802.11成立于IEEE项目下802推荐国际标准为无线本地局域网络（WLAN）。标准的最终版本最近出现了[3]，并提供了详细的媒体访问控制（MAC）和WLAN的物理层（PHY）规范。

在802.11协议中，访问该介质的基本机制称为分布式协调功能（DCF）。这是一种随机接入方案，具有碰撞避免（CSMA / CA）协议的多访问。回复相互影响的数据包的传输是根据双向二进制指数退避规则。该标准还定义了一个可选的点协调功能（PCF），这是一个集中式的MAC协议能够支持无碰撞和时间限制服务。在本文中，我们将调查限制DCF方案。

DCF描述了用于分组传输的两种技术。默认方案是双向握手技术称为基本访问机制。这种机制是字符由目的地站立即传递一个肯定的确认（ACK），成功接收由发送站发送的分组。需要ACK的任务，因为在无线介质中，发送器无法通过听自己的传播确定数据包是否成功接收。

除了基本的访问，一个可选的四路握手技术，被称为要发送/清除发送（RTS / CTS）机制已经标准化。发送前一个数据包，一个在RTS / CTS模式下运行的站“储备”该频道通过发送特殊的请求发送短帧。目的站确认收到RTS通过发送一个清除发送帧，之后发生正常的分组传输和ACK响应。以来碰撞只能发生在RTS帧上，并且被检测到由于缺乏CTS响应，RTS / CTS机制允许通过减少持续时间来提高系统性能当发送长消息时发生冲突。作为一个重要的副作用，RTS / CTS方案设计802.11协议适合打击所谓的问题隐藏式终端[4]，发生在移动对车站无法听到对方的声音。这个问题已经在[5]和[6]中得到了具体的考虑。另外，研究分组......

Abstract—Recently, the IEEE has standardized the 802.11 protocol for Wireless Local Area Networks. The primary medium access control (MAC) technique of 802.11 is called distributed coordination function (DCF). DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also ap-plies to a combination of the two schemes, in which packets longer

than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, in this paper we provide an extensive throughput performance evaluation of both ac-cess mechanisms of the 802.11 protocol.

Index Terms—802.11, collision avoidance, CSMA, performance evaluation.

I. INTRODUCTION

I N recent years, much interest has been involved in the design of wireless networks for local area communication [1], [2]. Study group 802.11 was formed under IEEE Project 802 to recommend an international standard for Wireless Local Area Networks (WLAN’s). The final version of the standard has recently appeared [3], and provides detailed medium access control (MAC) and physical layer (PHY) specification for WLAN’s.

In the 802.11 protocol, the fundamental mechanism to access the medium is called distributed coordination function (DCF).

This is a random access scheme, based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol. Re-transmission of collided packets is managed according to binary  xponential backoff rules. The standard also defines an optional point coordination function (PCF), which is a centralized

MAC protocol able to support collision free and time bounded services. In this paper we limit our investigation to the DCF scheme.

DCF describes two techniques to employ for packet transmis-sion. The default scheme is a two-way handshaking technique called basic access mechanism. This mechanism is character-ized by the immediate transmission of a positive acknowledge......